Reactivity of human saphenous veins at arterial perfusion pressures.

Vasospasm of human saphenous vein grafts has been reported after aorta-coronary bypass operations. However, it is unknown whether veno-arterial grafts are inherently responsive to vasoconstrictor stimuli after implantation into the arterial circulation or whether their vasomotion is secondary to hemodynamic changes. Thus in this study we used in vitro methods to directly evaluate whether isolated human saphenous vein segments respond to vasoconstrictor agents at arterial pressure levels. External diameter and intraluminal flow were monitored in 12 human saphenous vein segments, which were perfused at 30 ml/min with physiologic salt solution at 90, 70, and 50 mm Hg. Increasing intraluminal pressure higher than 50 mm Hg or exposing the vein to Ca(2+)-free media did not increase vessel external diameter or intraluminal flow, which suggests that human saphenous veins were fully distended at pressures of 50 mm Hg or greater. However, all human saphenous veins were activated by a 1 mumol/L dose of norepinephrine at 50 mm Hg and dilated during subsequent intraluminal infusion of a 1 mumol/L dose of acetylcholine, showing intact vascular smooth muscle and endothelial cell function. In the same vessels, a 1 mumol/L concentration of 5-hydroxytryptamine constricted human saphenous veins by 19%, 22%, and 26% at intraluminal pressures of 90, 70, and 50 mm Hg, respectively, and reduced vessel flow by 6%, 24%, and 42% at the same pressure levels. Similarly, a 1 mumol/L concentration of norepinephrine constricted vessels pressurized at 90, 70, and 50 mm Hg by 9%, 12%, and 17%, respectively, and attenuated vessel flow by as much as 32%. We conclude that human saphenous vein segments are fully distended at perfusion pressures greater than 50 mm Hg, but can dynamically constrict to vasoactive agonists and regulate graft flow at intraluminal pressures as high as 90 mm Hg. Our findings in isolated human saphenous vein segments lend support to clinical observations that human saphenous vein grafts should be regarded as vasoactive conduits after implantation at arterial pressure levels.

Comparison of saphenous vein graft relaxation between Plasma-Lyte solution and normal saline solution.

Venospasm of saphenous vein grafts may damage endothelial cells and compromise early and late graft performance. Hence it is desirable to identify and use storage solutions that minimize vascular spasm during vein preparation. In view of this, we initiated isometric tension-recording studies in isolated canine and human saphenous vein to evaluate the acute, vasoactive effects of two storage solutions, Plasma-Lyte solution and normal saline solution. In initial experiments, canine saphenous veins were mounted in tissue baths containing physiologic salt solution and tonically constricted by 2 x 10(-6) mol/L norepinephrine. The physiologic salt solution in the bath was then replaced by Plasma-Lyte solution or normal saline solution containing the same norepinephrine concentration, and changes in contraction amplitude were recorded for 90 minutes. Storage in Plasma-Lyte solution at 37 degrees C completely relaxed norepinephrine-activated canine saphenous vein within 20 minutes, whereas veins remained partially constricted in normal saline solution. Both Plasma-Lyte solution and normal saline solution relaxed canine saphenous vein less at room temperature (25 degrees C) than at 37 degrees C, implying that warming of storage solutions in the operating room may promote graft dilation. To identify the mechanism by which Plasma-Lyte solution induced relaxation, we replaced its putative vasodilator components of gluconate and acetate with NaCl, but this alteration did not reduce relaxation induced by Plasma-Lyte solution. However, adding 1.6 mmol/L CaCl2 to Plasma-Lyte solution completely reversed the venodilation, suggesting that the low Ca2+ content of Plasma-Lyte solution confers its relaxant action. Finally, we tested the vasoactive effect of Plasma-Lyte solution on human saphenous vein obtained by discard from coronary bypass operations. Plasma-Lyte solution at 37 degrees C effectively dilated norepinephrine-activated human saphenous vein, inducing complete relaxation within 20 minutes. On this basis, we recommend the use of Plasma-Lyte solution as a venodilating storage solution during coronary bypass operations to optimize vein graft relaxation before implantation.

Enhanced single-channel K+ current in arterial membranes from genetically hypertensive rats.

Arterial smooth muscle from hypertensive rats shows an increased membrane permeability to K+ that depends on Ca2+ influx. To define the mechanism of this membrane alteration, we tested the hypothesis that Ca(2+)-dependent K+ current (IK(Ca)) is increased in arterial muscle membranes from genetically hypertensive rats. Single-channel K+ currents measured in cell-attached and inside-out aortic membrane patches from spontaneously hypertensive rats (SHR) were compared with those from normotensive Wistar-Kyoto rats (WKY). Inside-out patches from both rat strains showed a predominant 225 pS, Ca(2+)- and voltage-dependent K+ channel in symmetrical 145 mM KCl solutions, which was blocked by tetraethylammonium [concentration for half-maximal block (IC50) < or = 0.3 mM]. In cell-attached patches of aortic muscle cells bathed in physiological salt solution, this channel [IK(Ca) channel] showed a fivefold higher open-state probability (NPo) in SHR as compared with WKY. This increased NPo of SHR IK(Ca) channels in membranes of intact aortic muscle cells was not correlated with an altered membrane potential in current-clamped SHR myocytes or with changes in cytosolic free Ca2+ concentration in fura-2-loaded aortic muscle cells. However, inside-out aortic membrane patches from SHR showed more detected IK(Ca) channels per patch, a higher IK(Ca) channel NPo, and a greater total patch current than their WKY counterparts. Further analysis revealed a greater Ca2+ sensitivity of SHR than WKY IK(Ca) channels. These results suggest that IK(Ca) channel function is altered in isolated membrane patches of arterial muscle from genetically hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of ambient temperature on papaverine-induced relaxations in canine saphenous veins.

This study was designed to measure the effect of ambient temperature (25 degrees C) on papaverine-induced relaxations in canine saphenous veins. Segments of vein were suspended in water-jacketed tissue baths at 37 degrees C, and isometric tension was recorded. After equilibration, veins were preconstricted by a median effective dose of norepinephrine 2 x 10(-6) mol/L at either 25 degrees C or 37 degrees C. Consequent dose-dependent relaxations showed that papaverine (10(-7) to 10(-3) mol/L was three times more potent as a dilator at 37 degrees C than at 25 degrees C, with half-maximal relaxations occurring at 2.2 x 10(-5) mol/L and 6.4 x 10(-5) mol/L, respectively. A 10(-4) mol/L dose of papaverine completely relaxed veins at 37 degrees C, whereas veins at 25 degrees C never fully relaxed even at ten times the standard concentration. In addition, the time for half-maximal relaxation with a 10(-4) mol/L dose of papaverine averaged 40 minutes at 25 degrees C compared with 22 minutes at 37 degrees C; this is indicative of a reduced relaxation rate at the lower temperature. These data show that papaverine is a slower and less potent dilator of canine saphenous veins at 25 degrees C than at 37 degrees C. This may have implications for the use of papaverine in the operating room, where it is usually applied at ambient temperature to reduce vasospasm of the saphenous vein during coronary artery bypass procedures.

A Ca(2+)-dependent K+ current is enhanced in arterial membranes of hypertensive rats.

This study was designed to investigate the role and regulation of arterial membrane K+ channels in hypertension. Aortic segments from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) were suspended for isometric tension recording. In other experiments, proximal aortic segments (PS) (exposed to high pressure) and distal aortic segments (DS) (exposed to lower pressure) were removed from surgically coarcted Sprague-Dawley rats and similarly prepared. Aortas from SHR and PS dose-dependently contracted to the K+ channel blocker tetraethylammonium (TEA) (0.1-10 mM), and this contraction was abolished by preincubation with 0.1 microM nifedipine. In contrast, the same concentrations of TEA did not contract either WKY or DS aortas. Since block of K+ channels by TEA had a different effect on aortic segments exposed to high versus low blood pressure, we compared whole-cell K+ currents in isolated vascular cells from the same aortas. The reversal potentials of depolarization-induced outward currents in WKY, SHR, DS, and PS aortic cells showed a Nernst relation to external K+ concentration indicative of selective K+ permeability. TEA (1 and 10 mM) was equipotent in blocking these K+ currents in patch-clamped cells from all aortic preparations, suggesting that the lack of TEA-induced contractions in WKY and DS aortas was not due to an absence of TEA-sensitive K+ channels in these arterial membranes. However, when the Ca2+ ionophore A23187 (10 microM) was used to increase the level of cytosolic Ca2+ in patch-clamped cells, the K+ current density in SHR and PS aortic cells was twofold or more higher than in WKY and DS cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of storage solutions on contraction and relaxation of isolated saphenous veins.

Saphenous veins are placed frequently in storage solutions before use as coronary bypass grafts. Controversy remains regarding which solution is optimal for the preservation of endothelium and vascular smooth muscle viability. Thus, this study measured the effect of four different storage solutions on saphenous vein smooth muscle and endothelial cell function. Saphenous vein segments from five baboons were stored for 3 h in one of four storage solutions consisting of physiological salt solution (PSS), University of Wisconsin solution (UWS), normal saline solution (NSS), or autologous whole blood (WB). Following storage, veins were suspended for isometric tension recording in tissue baths filled with PSS. Veins stored in PSS, UWS, and NSS showed similar contractile amplitude and agonist sensitivity to norepinephrine (10(-8) -10(-4) M) and KCl (20-100 mM). However, veins stored in WB contracted 31% less to KCl on average than those stored in the other three solutions (p < 0.05). The direct vascular muscle vasodilator, papaverine (10(-7) -10(-4) M), and the endothelium-dependent dilator, A23187 (10(-5) M), relaxed all vein preparations equally well. These results suggest that after storage in PSS, UWS, and NSS, contractile and relaxant vascular responses are similar in isolated saphenous veins. However, although veins stored in WB show comparable relaxation responses, they demonstrate an impaired vascular contraction immediately after storage. We conclude that storage of veins in blood may immediately modify vascular smooth muscle function.

Action spectra for bilirubin photodisappearance.

The excitation wavelength dependence of bilirubin photodestruction, as measured by quantum yields, has been determined in benzene, chloroform-1% ethanol, chloroform-1% hexane, methanol-1% concentrated ammonia, pH 8.5 aqueous buffer and pH 7.4 aqueous buffer with added albumin. The results show that in the visible spectrum the 370-490 nm excitation wavelength region is very effective in the photodestruction, but excitation in the UV-region (lambda less than 320 nm) is even more effective.

Photobilirubin: an early bilirubin photoproduct detected by absorbance difference spectroscopy.

Absorption of light converts bilirubin-IXalpha in solution to a mixture of what are probably cis-trans geometric isomers. This reaction is much faster than other photochemical reactions of bilirubin and reaches photoequilibrium before losses due to photooxidation are significant. At room temperature in the dark in the presence of trifluoroacetic acid or iodine or simply on standing, the photoproducts revert to the natural isomer. They also revert under visible light. Their formation and reversion can be followed by chromatography on polyamide and by absorbance difference spectroscopy.